Gearbox and disassembly method for disengaging a drive shaft in such a gearbox

ABSTRACT

A gearbox has a main unit and a secondary unit provided with respective casings of respective gear transmissions and with respective hollow shafts connected by means of a drive shaft; the secondary unit transfers motion between two axes forming an angle of less than 180° and which can be removed after having released the drive shaft; the drive shaft is engaged in an angularly fixed and axially sliding manner to the hollow shafts and is axially locked, at least in one direction, by means of an axial retaining device, which is releasable; the axial retaining device is coupled to one of the hollow shafts, at an axial end which is facing towards the other of the hollow shafts; at least one opening may be formed between the two casings, so as to access such an axial end and release the axial retaining device.

TECHNICAL FIELD

The present invention relates to a gearbox, in particular for turbofanjet engines in aeronautic applications.

BACKGROUND ART

Some engines of such a type have a gearbox comprising a secondary unit,of the bevel gear type, for transferring the motion between two inclinedaxes; and a main unit, which is connected to the secondary unit by meansof a drive shaft. In particular, the ends of such a drive shaft arecoupled, respectively, to hollow shafts belonging to the two aforesaidunits.

The hollow shaft of the main unit actuates an accessory assembly,arranged on the axial end opposite to the one into which the drive shaftis inserted. In other words, the main unit is axially interposed betweenthe accessory assembly and the drive shaft.

During maintenance operations, the gearbox is disassembled so as to beable to remove and/or treat the two units separately. Therefore, duringdisassembly, the drive shaft must be disengaged from the secondary unit.In particular, in the engines described above, the drive shaft isaxially extracted through the hollow shaft of the main unit, operatingfrom the accessory assembly side, after having disengaged and removedthe latter from the main unit.

However, this solution has some drawbacks. Indeed, the need to disengageand remove the accessory assembly implies relative long disassembly andmaintenance times. Furthermore, relatively large axial clearance isrequired at the side of the main unit in order to be able to gain easyaccess to the corresponding hollow shaft to disengage and extract thedrive shaft outwards.

In order to at least partially solve these drawbacks, the drive shaft inother turbofan jet engines is constituted by three or more pieces, whichare fixed to one another, e.g. by means of bolts, which may bedisengaged to disassemble and remove the drive shaft without need toremove the latter axially through the main unit. However, the fact ofmaking the drive shaft in several pieces complicates the making andassembly and the drive shaft itself. Therefore this type of solution isnot very satisfactory.

In U.S. Pat. No. 3,631,735, which corresponds to the preamble of claim1, the drive shaft comprises a splined portion which engages the hollowshaft of the main unit and is arranged in axial abutment against a ringarranged in a groove of such a hollow shaft. In use, such a ringprevents the drive shaft from being extracted from the hollow shaft ofthe main unit.

During disassembly, after having translated a cover, the ring can beaccessed to be removed. After having removed the ring, the drive shaftis extracted from the hollow shaft of the main unit and remains coupledto the secondary unit only. However, as mentioned above, it ispreferable to disengage the drive shaft out of the secondary unit,especially when it is the latter which is usually removed.

DISCLOSURE OF INVENTION

It is the object of the present invention to make a gearbox which allowsto solve the problems illustrated above in simple, cost-effectivemanner.

According to the present invention, a gearbox is provided, as disclosedin claim 1.

According to the present invention, a disassembly method for disengaginga drive shaft in such a gearbox is also provided, as disclosed in claim13.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the appendeddrawings which illustrate a non-limitative embodiment thereof, in which:

FIG. 1 shows a partial, simplified cross section of a preferredembodiment of the gearbox according to the present invention;

FIGS. 2 and 3 are enlargements of two details in FIG. 1;

FIG. 4 shows a perspective cutaway view of the detail which is enlargedin FIG. 3, during a step of the disassembly method according to apreferred embodiment of the present invention;

FIG. 5 is an axial view, with a shaft shown in cross section, of adetail in FIG. 4;

FIGS. 6 and 7 are similar to FIG. 1, and show other steps of thedisassembly method.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, reference numeral 1 indicates, as a whole, agearbox (shown partially and in simplified manner), in particular for aturbofan jet engine in aeronautic applications.

The gearbox 1 comprises a module or unit 2, generally indicated as“transfer gearbox” and comprising, in turn, a casing 3 and a geartransmission 4, which transmits motion between two inclined axes 5,6,i.e. which define an angle of less than 180° between each other. Inorder to perform this function, the transmission 4 is preferably definedby two bevel gears 7,8 which mesh each other.

The casing 3 is preferably constituted by several pieces fixed to oneanother, and houses the transmission 4 and two shafts 9,10, which aresupported by the casing 3 in known manner by means of rolling bearings.The shaft 9 extends along axis 5, defines a motion inlet, and supportsthe gear 7 in fixed position at an axial end thereof. The shaft 10,instead, extends along axis 6, defines a motion outlet, is axiallyhollow, is preferably made in one piece and axially ends with a portion11 which is fixed with respect to the gear 8. Preferably, the gear 8 ismade in only one piece with the portion 11.

With reference to FIG. 3, the shaft 10 ends on the end opposite toportion 11 with a portion 12, which defines an axial mouth 16 of theshaft 10, has a clutch, radially inwards, preferably defined by a holespline 13, and is joined to the portion 11 by means of an intermediateportion 14.

Furthermore, the shaft 10 comprises an inner projection 18, preferablydefined by an annular flange, which radially projects from the portion14 and has a function which will be described below.

With reference again to the FIG. 1, the gearbox 1 comprises a module orunit 22 (partially shown) generally indicated as “accessory gearbox”,and comprising, in turn, a casing 23 and a shaft 24, which extends alongaxis 6 within the casing 23, is axially hollow and is connected to theshaft 10 by means of a coaxial drive shaft 25.

The shaft 24 defines a motion inlet for a gear transmission 28 of theunit 22. The accompanying figures show only one of the transmissiongears 28, i.e. a gear which is indicated by reference numeral 29 andwhich is fitted onto shaft 24. In particular, the unit 22 is axiallyarranged between the shaft 25 and an accessory assembly (not shown),which is fixed to the casing 23 and is actuated (in manner not shown)either by the transmission 28 or by the shaft 24.

The shaft 24 axially ends, towards the accessory assembly, with aportion 31 and, towards the unit 2, with a portion 32, and comprises anintermediate portion 33 which has a clutch, radially inwards, alsopreferably defined by a hole spline 34. The hole splines 13 and 34 areengaged in an angularly fixed and axially slidable manner by shaftsplines, defined by a portion 35 (FIG. 3) and by a portion 36 (FIG. 2)of the shaft 25, respectively.

As shown in FIG. 2, the portion 32 is radially delimited by an externalthreaded surface 40 and by an inner surface 41, which extends startingfrom an axial end face 43 of the shaft 24 and is shaped so as to lock aring 44 which is at least partially housed in the portion 32 in angularmanner.

In particular, as shown in FIG. 4, the surface 41 comprises acylindrical zone 45 and at least one radial notch 46, which axiallyextends starting from the face 43.

The ring 44 is coaxial to the shafts 24 and 25, axially rests againstthe portion 32 and comprises an annular wall 48, coupled to the surface41 in an angularly fixed and axially sliding manner. In particular, thewall 48 has an external cylindrical surface 49, which is substantiallycomplementary with the zone 45, and comprises at least one radial tooth50, which projects outwards from the surface 49 and engages the notch 46for keeping the ring 44 angularly locked. Obviously, the number of thenotches 46 and of the teeth 50 may be higher. Alternatively to the notch46 and the tooth 50, different solutions may be provided for the angularlocking, e.g. respective flattenings on the surfaces 41 and 49.

The ring 44 further comprises an external flange 52, which projects froman axial edge of the wall 48 and has an external diameter which isgreater than the internal diameter of the face 43. The function of theflange 52 is to go against the face 43, and thus prevent the insertionof the ring 44 in the portion 32 if the ring 44 is fitted back to fronton the shaft 25 by mistake during the assembly operations of the gearbox1.

The ring 44 further comprises an axial shoulder 53, which is arranged onthe opposite axial end of the flange 52, and is advantageously definedby a hole spline or by an inner axial toothing 54, as shown in FIG. 5and as will be described hereinafter. The toothing 54 surrounds anintermediate portion 55 of the shaft 25 with radial clearance: in otherwords, the internal diameter of the axial shoulder 53 is greater thanthe external diameter of the portion 55.

Again with reference to FIG. 4, the portion 55 is preferably cylindricaland axially joins the portion 36 to an external radial projection of theshaft 25, advantageously defined by an axial toothing 56. In particular,the toothing 56 is identical and aligned with a shaft spline of theportion 36, so as to make both at the same time with the same method.

The toothing 56 projects from the portion 55 so as to reach an externaldiameter which is greater than the internal diameter of the shoulder 53,therefore the latter prevents the toothing 56 and, thus, the shaft 25,from translating axially towards the inside of the shaft 24.

It is thus apparent that the ring 44 and the toothing 56 constitute partof an axial retaining device 57, which prevents the axial sliding of theshaft 25 in direction opposite to the unit 2.

As shown in FIG. 5, if considered viewed along axis 6, the profiles incircumferential direction of the toothing 56 and of the shoulder 53 areshaped so as to be able to slide along axis 6 by the side of each otherwithout interference after a relative rotation, i.e. after a rotation ofthe ring 44 with respect to the shaft 25. Advantageously, the profile ofthe toothing 54, in circumferential direction, is complementary withthat of the toothing 56, but rotated by an amount substantially equal tohalf of the angular pitch between two consecutive teeth.

With reference to FIG. 2, the device 57 further comprises an axiallocking element 60, which is fixed to the portion 32 in releasablemanner and comprises a portion 61 which keeps the ring 40 engaged in theportion 32 in fixed axial position. Preferably, the locking element 60is defined by a ring nut which is fitted with slight radial clearanceabout the shaft 25 and is screwed onto the surface 40. In particular,the portion 61 is defined by an inner flange arranged on an axial end ofthe ring nut 60. Advantageously, the ring nut 60 has one or more radialholes 63 engaged by dowels (not shown), having an end engaging theportion 32 to perform an anti-loosening function on the ring nut 60.

Preferably, the shaft 25 is axially locked with respect to the shaft 24only one-way, because it is free to translate towards the unit 2. Inparticular, as shown in FIG. 3, within the unit 2, the shaft 25 has anend 64 which is axially spaced from the flange 18 and has an externaldiameter which is greater than the internal diameter of the flange 18.Thus, the latter defines a limit stop shoulder for the axial translationof the shaft 25.

Furthermore, the shaft 25 comprises an intermediate portion 65, whichaxially joins the portion 35 to the toothing 56, substantially has thesame external diameter as the portion 55 and carries an externalprojection 66. The projection 66 projects from the portion 65 so as toreach a diameter which is greater than the internal diameter of theportion 32, and has an axial position such to impede an incorrect backto front assembly of the shaft 25 (i.e. with the end 64 inserted in theshaft 24) during the assembly of the gearbox 1.

As shown in FIG. 1, the portion 65 of the shaft 25, the device 57 andthe axial mouth 16 of the shaft 10 remain enclosed by an annular shell70, which joins the casings 3 and 23, is either openable or removable soas to obtain at least an opening which is axially located between thecasings 3 and 23 and can provide access to the device 57 for releasingthe shaft 25 from the unit 2 during a disassembly procedure of thegearbox 1.

In particular, the shell 70 is of the telescopic type, because itcomprises two sleeves 72,73, which are substantially coaxial to theshaft 25, are fixed in releasable manner to the casings 3 and 23,respectively, and are coupled to each other in axially sliding manner.In practice, the sleeves 72,73 define respective doors, which areaxially sliding to define an opening 74 with respect to the casing 3(FIG. 7) and an opening 75 with respect to the casing 23 (FIG. 6),respectively.

With reference to FIG. 6, firstly the sleeve 73 is disengaged from thecasing 23 and then translated towards the unit 2 so as to form theopening 75 in the disassembly procedure, in order to release the shaft25 from the unit 2.

Subsequently, the device 57 is released by means of the followingoperations by manually operating through the opening 75:

-   -   the locking element 60 is disengaged and axially spaced from the        portion 32, so as to unlock the ring 44 axially;    -   the shaft 25 is translated towards the unit 2 so as to extract        part of the shaft 25 from the shaft 24; in particular, this        translation ends when the end 64 comes into contact with the        flange 18; in this manner, the toothing 56 is axially spaced        from the shoulder 53 by an amount sufficient to disengage the        ring 44 from the portion 32; preferably, the shaft spline of the        portion 36 continues to engage the hole spline after this        preliminary translation of the shaft 25;    -   the ring 44 is axially extracted from the portion 32 (FIG. 4) so        as to release the rotation of the ring 44 itself; in particular,        the ring 44 is taken into contact with the toothing 56 again;    -   the ring 44 is rotated about the shaft 25 so as to align the        toothing 54 axially with the voids of the toothing 56;    -   finally, the ring 44 is extracted along the toothing 54 so as to        move it away from portion 32 axially.

At this point, with reference to FIG. 7, the opening 75 is closed andthe sleeve 73 is fixed to the casing 23 again. The opening 74 is thenformed by disengaging the sleeve 72 from the casing 3 and moving itaxially away. Operating manually through the opening 74, the shaft 25 istranslated towards the unit 22, i.e. into the hollow shaft 24, so as torelease the shaft 25 from the hole spline 13 of the shaft 10.

It is apparent that, in this condition, the unit 2 is completelyseparated from the unit 22 and thus may be disengaged and removed, e.g.by means of a translation along axis 5, without interference with theunit 22 or with the shaft 25, while the shaft 25 remains coupled to theunit 22.

From the above, it is apparent that the configuration of the gearbox 1and, especially, the position of the device 57 allow to release theshaft 25 from the unit 2 without need to remove the accessory assemblyand without requiring clearance to operate on the unit 22 from the sideof the portion 31, because all the operations are carried out throughthe clearance which is axially available between the casings 3 and 23.Furthermore, the shaft 25 is disassembled without need to bedisassembled into several pieces, because it is simply made to slidealong the axis 6, first in one direction to generate a sufficientclearance to disengage the shoulder 53, and then in the oppositedirection to remove the shaft 25 from the unit 2 in effective manner.

In addition to relatively small clearance, the disassembly also requiresrelatively short times for releasing the shaft 25. In particular, thereare no bolts or screws to be unscrewed (except for the ring nut 60);there are no connection elements which need to be completely removed(indeed, the ring nut 60 and the ring 44, even after having beendisengaged from the portion 32, remain supported by the portion 65, asshown in FIG. 7, without the risk of loosing them in the shell 70 or inthe casings 3,23); and, as mentioned above, the shaft 25 does not needto be disassembled into several pieces.

In all cases, the features of the device 57 make the axial retention ofthe shaft 25 stable and safe, even if only one-way. At the same time,the features of the device 57 allow to have a relatively low number ofpieces with respect to the known solutions and thus to have a highsimplicity and a high reliability.

Finally, also the construction of the shaft 25 in one piece contributesto keep the number of components low.

From the above, it is apparent that changes and variations may be madeto the gearbox 1 without because of this departing from the scope ofprotection of the appended claims.

In particular, at least in principle, the device 57 could be arranged atthe mouth 16, instead of at the portion 32, so as to release the shaft25 from the unit 22 and insert it in the shaft 10. This solution ispreferable when the unit 22 is the one which is normally removed, whilethe shaft 25 remains coupled to the unit 2.

Furthermore, a two-way locking system may be provided (e.g. with apossible appendix of the ring nut 60 to lock possible axialdisplacements of the toothing 56 towards the unit 2), instead of aone-way system; and/or the ring nut 60 could be replaced by anotheraxial locking element (e.g. by an element fitted in radial direction onthe portion 32 or a bayonet-coupled element).

Furthermore, the shaft and hole splines provided between the shaft 25and shafts 10,24 could be replaced by other coupling systems which allowan angular constraint and axial sliding freedom in all cases.

Finally, the gearbox 1 could also be used for naval applications,instead of aeronautical applications.

The invention claimed is:
 1. A gearbox comprising: a main unitcomprising: a) a first casing; b) a first gear transmission; and c) afirst hollow shaft defining a motion input for said first geartransmission; a secondary unit comprising: a) a second casing; b) asecond gear transmission defining a transmission of motion between twoaxes forming an angle of less than 180°; and c) a second hollow shaftdefining a motion output for said second gear transmission; a driveshaft comprising a first and a second clutch portion, which respectivelyengage said first and second hollow shafts in an angularly fixed andaxially slidable manner to transmit motion from said second geartransmission to said first gear transmission; axial retaining means toprevent said drive shaft from translating axially in at least one of thetwo directions; said axial retaining means being releasable andcomprising an axial shoulder supported in fixed position by a portionwhich is defined by an axial end of one of said first and second hollowshafts and faces the other of said first and second hollow shafts;opening means provided between said first and second casing to accesssaid axial end and release said axial retaining means; wherein saidaxial retaining means further comprise an external radial projection,which is part of said drive shaft, is arranged in an intermediateposition between said first and second clutch portion and axially facessaid axial shoulder so as to prevent said drive shaft from translatingaxially towards said axial end.
 2. The gearbox according to claim 1,wherein the profiles in a circumferential direction of said externalradial projection and of said axial shoulder are shaped so as to enablethe drive shaft of sliding axially with respect to said axial shoulderin both directions after a relative rotation.
 3. The gearbox accordingto claim 2, wherein said axial retaining means comprise a ring, whichcomprises said axial shoulder, is arranged around a first intermediateportion of said drive shaft and is releasably fixed to said axial end.4. The gearbox according to claim 3, wherein said ring has a hole splinedefining said axial shoulder.
 5. The gearbox according to claim 3,wherein said ring is coupled to said axial end in an axially sliding andangularly fixed manner; said axial retaining means comprising an axiallocking means that keep said ring in an axially fixed position withrespect to said axial end.
 6. The gearbox according to claim 3, whereinsaid axial end is axially delimited by an end face and radiallydelimited by an inner surface; said ring comprising: an annular wallengaging said inner surface in an angularly fixed and axially slidingmanner, an external flange, which projects from an axial edge of saidannular wall and has an external diameter greater than the internaldiameter of said end face.
 7. The gearbox according to claim 1, whereinsaid external radial projection is defined by an axial toothingidentical to and aligned with a shaft spline defined by said firstclutch portion.
 8. The gearbox according to claim 1, wherein said axialretaining means are configured so as to prevent the axial translation ofsaid drive shaft only towards said axial end.
 9. The gearbox accordingto claim 1, wherein said other of said first and second hollow shaftscomprises an inner projection, which is axially spaced from said driveshaft and axially faces said drive shaft so as to define a limit stopshoulder.
 10. The gearbox according to claim 1, wherein said drive shaftcomprises a second intermediate portion provided with a further externalradial projection having dimensions and axial position such as toprevent back to front assembly of said gearbox.
 11. The gearboxaccording to claim 1, wherein said opening means are defined by anannular shell, which joins said first and second casing and is openableor removable.
 12. The gearbox according to claim 11, wherein saidannular shell comprises at least one closing element that is axiallyslidable to open an access towards the inside of said annular shell. 13.A disassembly method for disengaging a drive shaft in a gearbox madeaccording to claim 1, the method comprising the steps of: forming atleast one opening between said first and second casing; accessing saidaxial end through said opening to release said axial retaining meanswithout disassembling said drive shaft; the release of said axialretaining means comprising the following steps: a) partly extractingsaid drive shaft from said axial end so as to axially space saidexternal radial projection from said axial shoulder; b) disengaging saidaxial shoulder from said axial end; c) rotating said axial shoulder,with respect to said drive shaft, so as to prevent interference in axialdirection with respect to said external radial projection; axiallytranslating said drive shaft towards said axial end, by operatingthrough said opening, so as to disengage said drive shaft from saidother of said first and second hollow shaft, without disassembling saiddrive shaft.
 14. The disassembly method according to claim 13, whereindisengagement of said axial shoulder is carried out by: releasing axiallocking means, and axially extracting said axial shoulder from saidaxial end.
 15. The disassembly method according to claim 13, wherein,after rotation of said axial shoulder and before translation of saiddrive shaft, said axial shoulder is moved away from said axial end, withan axial sliding along said external radial projection.